An untreated flat glass surface reflects generally less than about 5% of the incident visible light. Its light reflective properties are known to be increased by application of a metallic or other coating to the surface. Special light- and heat-reflecting glasses have been manufactured in the past for glazing residential and industrial building structures as well as for window-equipped refrigeration and frozen product display units. Certain of these glasses are made or treated so as to reflect part of the visible light and to transmit another part. This type of glass will act as a mirror when looking at it from a lighted area to a darker space. Light transmission therethrough is good, however, when looking at it from a darker area to a brighter space.
Ceramic coatings were initially applied to glass as shields to protect personnel from intense long wave radiation and subsequently such ceramic coatings were developed for use on window glass. The transmittance for both visible and total solar radiation by such glasses can be varied over a fairly wide range.
Selective reflective coatings have also been applied to glass by vacuum evaporation of metals directly onto the glass surface. Such application involves an expensive batch process. Another known method for applying a selective coating to a glass surface is by chemical precipitation thereon of a film of such metals as iron, cobalt or nickel. This method is also quite costly and presents considerable difficulty in control of the extent of light transmission.
Preformed plastic sheets having opacifying or light-reflecting materials incorporated therein or applied to the surface of the plastic sheet, may be affixed to a glass surface to modify its light-transmitting properties.